ISO/IEC 18477-5:2018

INTERNATIONAL ISO/IEC
STANDARD 18477-5
First edition
2018-03
Information technology — Scalable
compression and coding of
continuous-tone still images —
Part 5:
Reference software
Technologies de l'information — Compression échelonnable et codage
d'images plates en ton continu —
Partie 5: Logiciel de référence
Reference number
ISO/IEC 18477-5:2018(E)
©
ISO/IEC 2018

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ISO/IEC 18477-5:2018(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
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ISO copyright office
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Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
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ISO/IEC 18477-5:2018(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 2
5 Conventions . 2
5.1 Conformance language . 2
5.2 Typesetting . 3
6 Reference software . 3
6.1 Purpose . 3
6.2 Examples of use . 3
6.3 General . 4
Annex A (informative) Unpacking and compiling the reference software for
ISO/IEC 18477-3 and ISO/IEC 18477-6 to ISO/IEC 18477-9 . 5
Annex B (informative) Using the reference software for ISO/IEC 18477-3 and
ISO/IEC 18477-6 to ISO/IEC 18477-9 . 6
Annex C (informative) Unpacking and compiling the reference software for
ISO/IEC 18477-7 profile B.12
Annex D (informative) Using the reference software for ISO/IEC 18477-7 profile B .13
Bibliography .17
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ISO/IEC 18477-5:2018(E)

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are
members of ISO or IEC participate in the development of International Standards through technical
committees established by the respective organization to deal with particular fields of technical
activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other international
organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the
work. In the field of information technology, ISO and IEC have established a joint technical committee,
ISO/IEC JTC 1.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for
the different types of document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject
of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent
rights. Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 29, Coding of audio, picture, multimedia and hypermedia information.
A list of all parts in the ISO/IEC 18477 series can be found on the ISO website.
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ISO/IEC 18477-5:2018(E)

Introduction
ISO/IEC 18477, also known under the name "JPEG XT", is a series of extensions of ISO/IEC 18477-
1, a compression system for continuous tone digital still images which is backwards compatible
with Rec. ITU-T T.81 | ISO/IEC 10918-1. That is, legacy applications conforming to Rec. ITU-T T.81 |
ISO/IEC 10918-1 will be able to reconstruct streams generated by an encoder conforming to the
ISO/IEC 18477 series, though will possibly not be able to reconstruct such streams in full dynamic
range, full quality or other features defined in the ISO/IEC 18477 series.
This document offers implementations of various parts of the ISO/IEC 18477 standard that demonstrate
the features and capabilities of JPEG XT. Its purpose is to act as a guideline for implementations and
as a reference for conformance testing. As such, the implementations are conforming to the part of
Rec. ITU-T T.81 | ISO/IEC 10918-1 that has been standardized as ISO/IEC 18477-1, i.e. it implements the
baseline, extended sequential and progressive Huffman coding modes of the legacy standard together
with common extensions such as Rec. ITU-T T.871 | ISO/IEC 10918-5, commonly known as JFIF. In
addition, the reference software implementations also cover all other parts of the ISO/IEC 18477
standard, i.e., IDR coding, HDR coding, lossless and near-lossless coding and coding of alpha channels.
This document includes the source code for reference implementations of the ISO/IEC 18477 series of
standards, available at http:// standards .iso .org/ iso -iec/ 18477/ -5/ ed -1/ en. They have been successfully
1) 2)
TM
complied and tested on Linux and Windows operating systems at the time of writing.
Note that ISO/IEC 18477-1 does not include the arithmetic coding modes, the hierarchical coding modes
and the lossless coding modes of Rec. ITU-T T.81 | ISO/IEC 10918-1.
1) Linux is an example of a suitable product available commercially. This information is given for the convenience
of users of this document and does not constitute an endorsement by ISO or IEC of this product.
2) Windows is an example of a suitable product available commercially. This information is given for the
convenience of users of this document and does not constitute an endorsement by ISO or IEC of this product.
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INTERNATIONAL STANDARD ISO/IEC 18477-5:2018(E)
Information technology — Scalable compression and
coding of continuous-tone still images —
Part 5:
Reference software
1 Scope
This document provides reference implementations of multiple parts of the ISO/IEC 18477 series, also
known under the name "JPEG XT". JPEG XT is designed primarily for compression of continuous-tone
photographic content.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO/IEC 18477-1, Information technology — Scalable compression and coding of continuous-tone still
images — Part 1: Scalable compression and coding of continuous-tone still images
ISO/IEC 18477-3, Information technology — Scalable compression and coding of continuous-tone still
images — Part 3: Box file format
ISO/IEC 18477-6, Information technology — Scalable compression and coding of continuous-tone still
images — Part 6: IDR Integer Coding
ISO/IEC 18477-7, Information technology — Scalable compression and coding of continuous-tone still
images — Part 7: HDR Floating-Point Coding
ISO/IEC 18477-8, Information technology — Scalable compression and coding of continuous-tone still
images — Part 8: Lossless and near-lossless coding
ISO/IEC 18477-9, Information technology — Scalable compression and coding of continuous-tone still
images — Part 9: Alpha channel coding
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
3.1
codestream
sequence of bytes that conforms to or is to be checked for conformance with the codestream syntax
specified in ISO/IEC 18477-1 and/or ISO/IEC 18477-3
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3.2
decoder
embodiment of the decoding process specified in the ISO/IEC 18477 series or a process embodiment
that is to be tested for conformance to the ISO/IEC 18477 series
3.3
encoder
process that produces codestreams (3.1) that conform to ISO/IEC 18477-1 or ISO/IEC 18477-3 or that
are to be tested for conformance to the ISO/IEC 18477 series
3.4
pfm format
format similar to ppm (3.6) for carrying floating-point based colour images
Note 1 to entry: It is further specified in ISO/IEC 18477-4.
3.5
pnm format
superset of the pfm (3.4) and ppm format (3.6)
3.6
ppm format
portable pixmap format for carrying three-component integer sample based colour images specified in
ISO/IEC 18477-4
4 Abbreviated terms
HDR high dynamic range
IDR intermediate dynamic range
LDR low dynamic range
PPM portable pixmap format
PFM portable floating-point format
TMO tone mapping operator
5 Conventions
5.1 Conformance language
This document consists of normative and informative text.
Normative text is that text which expresses mandatory requirements. The word "shall" is used to
express mandatory requirements strictly to be followed in order to conform to this document and
from which no deviation is permitted. A conforming implementation is one that fulfils all mandatory
requirements.
Informative text is text that is potentially helpful to the user, but not indispensable and can be removed,
changed or added editorially without affecting interoperability. All text in document is normative,
with the following exceptions: the Introduction, any parts of the text that are explicitly labelled as
"informative" and statements appearing with the preamble "NOTE" and behaviour described using the
word "should". The word "should" is used to describe behaviour that is encouraged but is not required
for conformance to this document.
The keywords "may" and "need not" indicate a course of action that is permissible in a conforming
implementation.
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The keyword "reserved" indicates a provision that is not specified at this time, shall not be used and
may be specified in the future. The keyword "forbidden" indicates "reserved" and in addition indicates
that the provision will never be specified in the future.
5.2 Typesetting
Regular face fonts as this text describe informative text that provides instructions, comments or details
for the reader.
Monospaced text as this paragraph indicates program input or output as necessary to either
run the software or as generated by the software on the console.
6 Reference software
6.1 Purpose
The purpose of this document is to provide the following.
— Reference decoder software capable of decoding codestreams that conform to ISO/IEC 18477-1,
ISO/IEC 18477-3, ISO/IEC 18477-6, ISO/IEC 18477-7, ISO/IEC 18477-8 and/or ISO/IEC 18477-9.
— Sample encoder software capable of producing codestreams that conform to one or multiple parts
of the ISO/IEC 18477 series.
The use of the reference software is not required for making an implementation of an encoder or
decoder in conformance to any of the ISO/IEC 18477 series. Requirements established in ISO/IEC 18477-
1, ISO/IEC 18477-3, ISO/IEC 18477-6, ISO/IEC 18477-7, ISO/IEC 18477-8 and ISO/IEC 18477-9 take
precedence over the behaviour of the reference software.
6.2 Examples of use
Some examples of use for the reference decoder software implementations are as follows:
— as an illustration of how to perform the decoding processes specified in one or multiple parts of the
ISO/IEC 18477 series;
— as the starting basis for the implementation of a decoder that conforms to one or multiple parts of
the ISO/IEC 18477 series;
— for testing the conformance of a decoder implementation of one or multiple parts of the ISO/IEC 18477
series with the procedures specified in ISO/IEC 18477-4. Details on reference testing can be found
in ISO/IEC 18477-4;
— for (non-exhaustive) testing of the conformance of a codestream (or file) to the constraints specified
in ISO/IEC 18477-3, ISO/IEC 18477-6, ISO/IEC 18477-7, ISO/IEC 18477-8 or ISO/IEC 18477-9.
NOTE 1 Attempting to decode a codestream under testing with a reference software implementation
implements only a non-exhaustive test for conformance. The lack of detection of any conformance violation by
any reference software implementation can therefore not be considered as a definite proof that the codestream
under testing conforms to all constraints required for it to be conforming to one of the ISO/IEC 18477 standards.
Some examples of use for a reference encoder software are as follows:
— as an illustration of how to implement an encoding process that produces codestreams that are,
depending on the settings of the software, conforming to one or multiple members of the software
of the ISO/IEC 18477 series;
— as starting point for an implementation of an encoder that conforms to one or multiple members of
the ISO/IEC 18477 series;
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— as a means of generating codestreams conforming to one or multiple parts of the ISO/IEC 18477
series for testing purposes;
— as a means of demonstrating and evaluating examples of the quality that can be achieved by an
encoding process that conforms to multiple parts of the ISO/IEC 18477 series.
NOTE 2 However, no guarantee of the quality that will be achieved by an encoder is provided by its
conformance to one or multiple parts of the ISO/IEC 18477 series as the conformance is only defined in terms
of specific constraints imposed on the syntax of the generated codestream. In particular, while sample encoder
software implementations may suffice to provide some illustrative examples of which quality can be achieved
within the ISO/IEC 18477 series, they provide neither an assurance of minimum guaranteed image encoding
quality nor maximum achievable image encoding quality.
NOTE 3 Similarly, the computation resource characteristics in terms of program or data memory usage,
execution speed, etc. of sample software encoder or decoder implementations cannot be construed as a
representative of the typical, minimal or maximal computational resource characteristics to be exhibited by
implementations of some parts of the ISO/IEC 18477 series.
6.3 General
The reference software implementations for the ISO/IEC 18477 series are provided at http:// standards
.iso .org/ iso -iec/ 18477/ -5/ ed -1/ en.
— The file "reference1367abcd89.zip" contains a reference implementation for ISO/IEC 18477-1,
ISO/IEC 18477-3, ISO/IEC 18477-6, ISO/IEC 18477-7 profiles A, B, C and D, ISO/IEC 18477-8 and
ISO/IEC 18477-9. Unpacking and compilation of this software is explained in Annex A and guidance
on how to use this software is given in Annex B.
— The file "reference7b.zip" contains a reference implementation for ISO/IEC 18477-7 profiles B.
Unpacking and compilation of this software is explained in Annex C and guidance on how to use this
software is given in Annex D.
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ISO/IEC 18477-5:2018(E)

Annex A
(informative)

Unpacking and compiling the reference software for
ISO/IEC 18477-3 and ISO/IEC 18477-6 to ISO/IEC 18477-9
The source code of the software is provided in a ZIP archive at http:// standards .iso .org/ iso -iec/ 18477/
-5/ ed -1/ en. Unpacking a ZIP file is operating system specific. Under POSIX compliant operating systems,
open a command line window and enter
unzip reference1367abcd89.zip
This will unpack all components of the software into the current directory.
To compile the software, follow these steps:
—  For POSIX compliant operating systems, change into the directory the electronic
attachment was unpacked into, then enter on the command line
./configure
make
This assumes that a POSIX compliant shell is available and the GNU compiler (make,
gcc compiler and linker) are installed on the system. The reference software will
then be built in the current directory and a binary named “jpeg” will be created.
TM2) 4) TM TM
—  For Microsoft Windows , the Visual Studio VS2010 or VS2013
compiler suite provides another option for compling the software. A VS2010 solution
file allowing loading and compiling the project can be found in the directory “vs10.0/
jpeg”. A solution file for VS2013 can be found in the directory “vs12.0/jpeg”.
The compiler will generate a command line tool without any graphical interface that compresses images
represented in pnm (Picture AnyMap) into JPEG XT and expands JPEG XT images into pnm-files. pnm-
files can either represent integer colour data, using the .ppm file extension or floating-point data using
the .pfm extension. The .ppm files contain three (or one) big-endian integers per pixel and the .pfm files
three (or one) 32-bit IEC big-endian floating-point integers. Converting these formats to other formats
is out of the scope of this document.
NOTE Some implementations of PPM or PFM readers use little-endian encoding or save the image bitmap
upside down, i.e. with the bottom line of the image included as first data in the file. Such encodings are not
supported by this software.
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ISO/IEC 18477-5:2018(E)

Annex B
(informative)

Using the reference software for ISO/IEC 18477-3 and
ISO/IEC 18477-6 to ISO/IEC 18477-9
B.1 General
This annex describes the usage of the software contained in the file reference1367abcd89.zip and
prepared and compiled with the instructions given in Annex A.
The software can both compress images to JPEG XT files and expand such files back to pnm. The
compressor and decompressor are both contained in the same executable named “jpeg”. If a quality
parameter (see below) is included on the command line or the command line parameters request
lossless coding, the executable encodes images. If only an input and an output file are provided, the
software attempts to expand the input file to the output file.
The compressor requires either one or two input images, both encoded in the ppm format. The first
image is the HDR or IDR image, i.e. the original image that is to be compressed. The second image, to be
provided as argument to the -ldr command line parameter, defines an 8-bit LDR image that defines
the base image legacy implementations of Rec. ITU-T T.81 | ISO/IEC 10918-1 will fall back to.
If the -ldr command line parameter is omitted, the software itself creates an 8-bit tonemapped
version of the input. It is noted that the images generated by the simple built-in operator are not ideal
and external tonemappers are preferable for better results. Encoding the LDR/HDR image depends on
the base image, containing the LDR image and an extension layer that allows the decoder to reconstruct
an approximate version of the original image from the LDR image and the extension layer. Both base
image and extension layer are controlled by independent quantizers, both of which are controlled by
the command line through “quality” parameters.
The compressor also allows specifying separate quality parameters for the tonemapped image and the
original image. Alternatively, a very simple built-in rate-allocation can provide a reasonable default for
the quality selection between tonemapped and original image compressor.
The command line parameters for the compressors are as follows:
jpeg [options] source target
where options is a set of command line options, all starting with a dash, source is the source image
to be expanded or compressed and target is the output file the compressor or expander provides
its output in. Command line switches control the operations of the software. They are listed in the
following subclauses.
Decoding from an JPEG XT file to a ppm or pfm file requires only the input and output file name:
jpeg [options] source target
The only command line option recognized for decoding is -c, which disables the transformation from
YcbCr to RGB.
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B.2 Options defining the quality of the base and full image and of the alpha channel
The following options control the quality of the encoded images.
-q quality selects the encoding mode and defines the quality of the
base image
-Q quality defines the quality of the extension layer
-quality q uses a profile and part specific weighting between base and
extension layer quality
-l enables lossless coding without a residual image by an int-
to-int DCT, also requires -c and -q 100 for true lossless
-rl    enforces a int-to-int lossless DCT in the residual domain,
for lossless coding enabled by -Q 100
B.3 Options defining the base image
The following options control the base image and its creation.
-ldr file specifies a separate file containing the base layer for
encoding
-g gamma defines the exponent for the gamma for the LDR domain, or
rather, for mapping HDR to LDR. A suggested value is 2.4
for mapping scRGB to sRBG.
This option is only used if -ldr is missing to generate
an LDR image from the HDR input. Use -g 0 for automatic
tonemapping.
-gf file defines the inverse one-point L-nonlinearity on decoding
from a file
This file contains one (ASCII encoded) digit per line,
256*2^h lines in total, where h is the number of refinement
bits. Each line contains an (integer) output value the
corresponding input is mapped to.
-e exposure defines a manual exposure value for part 7 profile B. Auto-
exposure, i.e. not using this parameter, is recommended.
-ae factor defines an auto-exposure value for part 7 profile B. By
default, this factor is 0.6.
B.4 Options controlling the colourspace
The following options control how out of gamut colours and gamut extension is handled.
-c     disables the RGB to YcbCr decorrelation transformation
-xyz indicates that the HDR image is in the XYZ colourspace.
Note that the image is not converted to this space, but is
assumed to be encoded in this space.
-cxyz   similar to above, but uses the dedicated C transformation
to implement a XYZ colourspace conversion.
-ncl    disables clamping of out-of-gamut colours. This is
automatically enabled for lossless.
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B.5 Options controlling the generation of additional JPEG XT specific scans
The following options control the generation of additional scans including additional data to enhance
the bit precision. All parts and profiles that include a residual codestream, most notably all profiles of
ISO/IEC 18477-7 except profile D, require the specification of the -r command line option to trigger the
computation of a residual.
-r enables the residual codestream for HDR and lossless
coding, requires -q and -Q to define base and enhancement
layer quality
-r12 uses a 12 bit residual image instead of an 8 bit
residual image
-R bits specifies refinement bits for the base image. This works like
-r but in the DCT domain
-rR bits specifies refinement bits for the residual image
B.6 Options controlling the profile and part
By default, the encoder creates an ISO/IEC 18477-1 conforming file. If the -r,-l or -R options are given,
the part it complies to depends on additional parameters. With integer (ppm) input files, the output is
conforming to ISO/IEC 18477-6. With -r -Q 100 or with -l -q 100 -c, the output is conforming
to ISO/IEC 18477-8. For floating-point input, the profile is specified by an additional command line
parameter.
-profile X encodes according to profile X, X = a, b, c, d as defined in
the JPEG XT standard. Without any parameter, the encoder
tries to figure out the profile itself.

B.7 Options controlling the scan generation and entropy coding
The following parameters control the entropy coding and generation of scan patterns for JPEG and
JPEG XT scans. Especially, the -h parameter (optimize Huffman tables) is recommended and for most
configurations, even necessary as the legacy JPEG standard does not provide examples for default tables
for most extended modes.
-h optimizes the Huffman tables
-v uses progressive instead of sequential encoding, available
for all coding schemes (-r,-a,-l and default)
-qv uses a simplified scan pattern for progressive that only AC
from DC bands and may improve the performance
-rv    encodes the residual image in progressive coding mode.
-rs encodes the residual image in sequential (rather than the
modified residual)coding mode
-ro disables the DCT in the residual domain, quantizes
spatially for near-lossless coding
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B.8 Options controlling the quantizer
The following parameters control the quantizer of both the base and the extension layer.
-qt n defines the quantization table. The following tables are
currently defined:
—  n = 0 the default tables from Annex K of
the JPEG standard (default)
—  n = 1 a completely flat table that should be
PSNR-optimal
—  n = 2 a MS-SSIM optimized table
—  n = 3 the table suggested by ImageMagick
—  n = 4 a HSV-PSNR optimized table
—  n = 5 the table from Klein, Silverstein and
Carney: Relevance of human vision to JPEG-DCT
compression (1992)
—  n = 6 the table from Watson, Taylor,
Borthwic
...